Field of the Disclosure
This disclosure relates to superconductors and more specifically to the mechanical and electrical properties of superconducting tapes.
Background of the Disclosure
Several materials and systems have been researched in order to solve the future problems with energy generation, transmission, conversion, storage, and use. Among many potential solutions, superconductors may represent a unique system solution across a broad spectrum of energy problems. More specifically, superconducting structures, including high-temperature superconducting (HTS) tapes, enable high efficiencies in generators, power transmission cables, motors, transformers and energy storage. Further, superconductors may have applications beyond energy to medicine, particle physics, communications, and transportation.
Conventionally, there are about nine components in a typical second-generation high-temperature superconducting (2G HTS) tape. The architecture consists of several oxide films on a metallic substrate and capped with silver and copper over-layers. The composite structure is prone to issues such as debonding between individual layers and delamination within the superconductor layer. Transverse tensile strength measurements on some conventional 2G HTS tapes, wherein a tensile stress is applied normal to the tape's surface, have shown evidence of weakness. A uniform pull or stress may be imparted on the tape by means of Lorentz force acting mutually perpendicular to a transport current flowing through a superconducting tape in conjunction with an externally applied magnetic field. The fracture surfaces of the 2G HTS tape provide insight into the interfaces and films architecture or structures that are prone to debonding and delamination. More specifically, the interface between the LaMnO3 (LMO) top buffer layer and the REBa2Cu3Ox (REBCO) superconducting film has been found to be prone to debonding and the REBCO itself has been observed to be prone to delamination within the overall architecture of the HTS tape.
Additionally, evidence of weak transverse strength in tapes in coils fabricated with epoxy impregnation has been observed. The difference in thermal expansion coefficients of the tape and epoxy may result in the transverse stress on the tape. Thus, if the tolerance of the tape to this stress is low, then coil degradation may occur. Further, as a significant proportion of the applications of 2G HTS tape involve coil geometries, this mechanical weakness poses a significant problem in the deployment of 2G HTS tapes to these industries. Another source of weakness within the REBCO film structures is the presence of secondary phases, such as copper-oxide (CuO) and misoriented a-axis grains. These inhomogeneities in the microstructure provide crack propagation paths that may result in reduced transverse tensile strength, as well as decreased current carrying capacity, or critical current, of the superconductor, and may be detrimental to other electrical properties. Thus, there is a demand for a HTS tape having improved transverse tensile strength and electrical properties for commercial applications.